High-Resolution Gridded MOS (HRMOS) QPF Guidance: Part I

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High-Resolution Gridded MOS (HRMOS) QPF Guidance
Part I Description of Products

• Jess Charba
• Fred Samplatsky
• Meteorological Development Laboratory
• OST / NWS / NOAA

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Motivation for HRMOS QPF Model

• Predictive skill of model- and human-produced
  QPFs lags skill of other atmospheric variables
  and weather elements
• Recent availability of fine grid radar-based
  precipitation data offers potential for improved
  MOS-based gridded QPF guidance
• Improved guidance should exhibit improved spatial
  and intensity resolution

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HRMOS QPF Model Basics

• Produces GFS-based MOS QPF guidance on a 2.5-km
  grid (4 km presently) for CONUS
• New QPF products contain better spatial and
  intensity resolution than other numerical and
  statistical model QPF guidance
• New QPF products exhibit equal or higher skill
  than comparable products
• HRMOS model issues conventional and new QPF
  products

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HRMOS QPF Products

• 6- 12-h QPFs to 192 hours on 2.5 km grid over
  CONUS
• Produced (experimentally) twice per day by 0530
  and 1730 Z
• QPF products
• - Probabilities for precip thresholds
• - Categorical precip amount
• - Continuous precip amount (web scores at
  http//www.weather.gov/mdl/hrqpf/verif.php)
• - Prob-weighted precip amount

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Probability (Prob) QPF

Probs for eight 6-h precip thresholds which range
from 0.01 to 2.00 For 12-h period probs
issued only for 0.01 (POP) Probs decrease with
increasing threshold and projection Probs are
basic other three QPF products are derived from
them http//www.weather.gov/mdl/hrqpf/gridded.php
and example prob maps
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0.01 in.
0.25 in.
84-h Prob () for 18-00 z 18 Apr 2009
(Note scale chgs in these maps)
1.00 in.
2.00 in.
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Categorical Precip (Cat) QPF
Derived from probs along with pre-determined
threshold probs - Prob thresholds vary by
precip threshold, geography, and projection -
Where prob thresholds are met for multiple precip
thresholds, precip category selection algorithm
applied to obtain Cat QPF Cat QPF has bias of
1.2 (perfect bias 1.0) for all precip
thresholds and projections http//www.weather.gov
/mdl/hrqpf/gridded.php and example maps of Cat
QPF and Probs

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Spatial pattern uniqueness for Cat QPF due to
localized prob thresholds
Cat QPF (in.)
Prob () 0.25 in.
84-h Cat Prob QPFs for 18-00 z 18 Apr 2009
Prob () 1.00 in.
Prob () 2.00 in.
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Continuous (Cont) QPF
Derived from Cat QPF by interpolating between
(bounded) categories and extrapolating above
top category - use multi-variate algebraic
formulae - variables are probs, prob
thresholds, categorical precip bounds, max prob
and upper bound for 2.00 in. category Max Cont
QPF for 6-h period is 4.75 in. (7.0 in. for 12-h
period) http//www.weather.gov/mdl/hrqpf/gridded.
php and example maps of Cont and Cat QPF

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Note - spatial pattern similarity of Cont QPF
to Cat QPF - extrapolation above top category
Cont QPF (in.)
84-h QPFs for 18-00 z 18 Apr 2009
Cat QPF (in.)
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Prob Weighted (Prob Wtd) QPF

• Computed from probs for bounded precip intervals
  (computed) and conditional means for precip
  intervals (pre-determined)
• Contains non-zero values where precip (of any
  intensity) is a threat
• Has tendency to spread low values over broad
  areas
• High values are generally much lower than for
  Cont QPF
• http//www.weather.gov/mdl/hrqpf/gridded.php and
  example maps of Prob Wtd, Prob, Cont QPF

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Prob Wtd QPF shows - spatial pattern
similarity to Prob QPF - spatial pattern and
magnitude contrasts to Cont QPF - lower peak
values than Cont QPF and Obs
Prob Wtd QPF (in.)
Prob () 0.25 in.
84-h QPFs Obs for 18-00 z 18 Apr 2009
Cont QPF (in.)
Obs (in.)
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HRMOS QPF Strengths

• High spatial resolution in locations with local
  precip forcing, based on
• - hi-res precip climatology
• - hi-res topography
• Example

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Note precip amt scale chg
Prob () 0.50 in.
Prob Wtd QPF (in.)
Obs (in.)
Cont QPF (in.)
84-h QPFs Obs for 18-00 z 05 Jan 2008
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HRMOS QPF Strengths (Cont)

• High precip intensity resolution (for
  extra-tropical and tropical systems) due to
• - high precip thresholds
• - geographical regionalization of model
• - smart extrapolation of Cat QPF above top
  threshold
• Example

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Extra-tropical 18-h QPF Obs for 00-06 z 19
Mar 2008
Cont QPF (in.)
Obs (in.)
Extra-tropical Tropical 72-h QPF Obs for
06-12 z 13 Sep 2008
HUR. IKE
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HRMOS QPF Strengths (Cont)

• Prob and Prob Wtd QPFs show high consistency
  across forecast projections and cycles

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HRMOS QPF Weaknesses

• Probs drop off rapidly with increasing precip
  thresholds
• Cat and Cont QPFs tend to
• - fluctuate excessively across consecutive
  projections for a given cycle
• - fluctuate excessively across consecutive
  cycles for a given valid period
• - example / fix for problem in progress
• All QPF products tend to over-forecast heavy
  precip events in the northern US and
  under-forecast in the southern US
• All QPF products tend to under-forecast
  development of intense convection along southern
  flank of cold fronts
• Examples of over/under-prediction

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84-h QPF for 18-00 z 18 Apr 2009
Over-fcst in KS, NE Under-fcst E TX
Cont QPF (in.)
Obs (in.)
42-h QPF for 12-18 z 28 Mar 2009
Over-fcst in E TN Under-fcst S AL, GA
Cont QPF (in.)
Obs (in.)
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Targeted Users of HRMOS Guidance

• NCEP/HPC
• WFOs
• RFCs
• External customers/partners

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Real-time HRMOS QPF Availability

• Downloadable Grib2 files at http//www.weather.gov
  /mdl/hrqpf/
• Graphical charts (including comparative QPF
  products) at same website
• Operational ingest into AWIPS is work in progress

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Implementation Plan

• Replace and supplement GMOS QPF guidance over
  CONUS
• Operational deployment FY 2010

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User Feedback

• Feedback alternatives at http//www.weather.gov/md
  l/hrqpf/
• - Comments and Suggestions link
• - Contact Us link
• - Join the Mailing List link
• Your constructive comments are welcome and
  appreciated

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END